The present invention describes improved polyestercarbonates and methods for their synthesis that involves the incorporation of structural units derived from carboxylic acids and their derivatives into polycarbonate chains under solid state polymerization (SSP) conditions. These acids include branched diacids, diacid soft blocks, and p-hydroxybenzoic acid (PHB), preferably, phenyl p-hydroxybenzoate. The present invention also preferably employs a catalyst, Sb2O3, and diphenyl carbonate in the production of the improved polyestercarbonates. Using the method of the present invention aromatic triacids such as the trisphenyl ester of 1,3,5-benzenetricarboxylic acid, a branching agent, may also be incorporated into these precursors before subjecting the precursor to SSP to produce branched polycarbonates. Following SSP, the resulting polyestercarbonates exhibit superior physical characteristics such as improved flow or enhanced melt strength, and modified Tg in comparison to analogous polycarbonate compositions lacking ester linkages.
Traditionally, two techniques were utilized in the production of polyestercarbonates: interfacial polycondensation processes and melt phase carbonate interchange reactions. Interfacial polycondensation routes to polyestercarbonates involve contacting a bisphenol and a diacid or diacid chloride with phosgene in a mixed aqueous-organic solution. An acid acceptor and optionally a catalytic amine are also present.
Interfacial polycondensation processes suffer several disadvantages. First, toxic and hazardous phosgene is utilized in these reactions. Also, the interfacial polycondensation process employs a chlorinated hydrocarbon, such as methylene chloride, as the organic solvent which requires substantial and costly environmental management to prevent unintended solvent emissions. Furthermore, the product polyestercarbonate contains residual sodium and chloride ions which adversely affect the hydrolytic stability of the product.
Methods for the preparation of polyestercarbonates through melt phase carbonate interchange reactions are also known. In a typical melt phase process, a bisphenol and a diacid or diester is contacted with a diaryl carbonate in the melt in the presence of a suitable catalyst. An oligomeric polyestercarbonate is produced, usually with a weight average molecular weight in the range of 2,000-10,000 daltons as determined by gel permeation chromatography, which may be relative to polycarbonate or polystyrene standards. The oligomer generally has an intrinsic viscosity between 0.06 and 0.30 dl/g as determined in chloroform at 25xc2x0 C. The oligomer is then converted to a high molecular weight polyestercarbonate by increasing the polymerization temperature.
Melt phase processes also suffer from a number of disadvantages. For example, at very high conversions ( greater than 98%), the melt viscosity increases considerably. Handling of high viscosity melt polymerization mixtures at high temperature is difficult. There is an increased chance of poor mixing and generating hot spots, which lead to the loss of product quality. In addition, this route requires specially designed equipment such as a Helicone mixer operating at temperatures in the range of 270-300xc2x0 C. Polyestercarbonates are susceptible to degradation at high temperature to a greater extent than are homopolycarbonates.
More recently, SSP has been used as an alternative process for the preparation of high molecular weight polycarbonates. SSP utilizes substantially lower temperatures than the melt process. Typically SSP is carried out in a range between about 180 and about 230xc2x0 C. The SSP process does not require handling molten polymer (melt) at high temperatures and the equipment needed to perform the reaction is very simple. In a typical solid state polycondensation process, a suitable polycarbonate oligomer is subjected to programmed heating above the glass transition temperature of the polymer but below its sticking temperature with removal of the volatile by-product. The polycondensation reaction proceeds strictly in the solid state under these conditions.
The SSP process is typically conducted in two stages. In the first stage, a low melt viscosity linear polycarbonate oligomer is synthesized by the melt phase reaction of a bisphenol with diaryl carbonate. Usually, a mixture of a dihydroxydiaryl compound and a diaryl carbonate is heated at 150xc2x0 C. to 325xc2x0 C. for 4 to 10 hours in presence of a transesterification catalyst to prepare an oligomer having weight average molecular weight of 2,000-10,000 daltons and having both hydroxyl and carbonate end groups. This oligomeric polycarbonate is referred to as the precursor or precursor polycarbonate. Thereafter, crystallization of the linear polycarbonate oligomer may be effected either by (a) dissolving the oligomer in a solvent and evaporating the solvent in presence of a suitable catalyst or (b) suspending the oligomer in diluent and refluxing it for 0 to 10 hrs in presence of a suitable catalyst followed by evaporating the diluent or (c) heating the oligomer at a temperature which is higher than the glass transition temperature of the oligomeric polycarbonate undergoing crystallization but below its melting point, in the presence of a suitable catalyst. It has been observed that diphenyl carbonate serves as a crystallization aid during thermal crystallization. Illustrative solvents and diluants include aliphatic aromatic hydrocarbons, ethers, esters, ketones, and halogenated aliphatic and aromatic hydrocarbons. The resulting oligomer has a crystallinity of between 5% and 55% as measured by a differential scanning calorimeter.
In a typical process, SSP, sometimes referred to as solid state polycondensation, is carried out by heating the crystallized oligomer along with a suitable catalyst. The reaction temperature and time may vary according to the type (chemical structure, molecular weight, etc.) of crystallized oligomer. However, it should be at least above the glass transition temperature and below the melting or sticking point of the oligomer. At this temperature the oligomer should not fuse during the solid state polycondensation. Since the melting point of the crystallized oligomer increases during the course of polycondensation, it is therefore desirable to increase the polycondensation temperature gradually. Generally the temperature should be 10-50xc2x0 C. below the melting point of the oligomer and it should be in the range of 150-250xc2x0 C. and more preferably between 180 and 220xc2x0 C.
During the process of solid state polycondensation, the by-products (e.g. phenol, diphenyl carbonate, bisphenol) should be removed from the reaction system so as to allow the reaction to progress. For this purpose an inert gas is passed through the system which carries out the by-product. The inert gases which are generally used are N2, He, Ar etc. and the flow rate of the carrier gas varies from 0.1 to 4 L/min depending upon the type of reactor and the particle size of the oligomer. The rate of polycondensation may depend on the type and the flow rate of the carrier gas.
Certain types of monomers are usually preferred for providing aliphatic ester units in polyestercarbonates prepared using the interfacial and melt preparation methods. One known method uses aliphatic alpha omega dicarboxylic acids that contain between 8 and 20 carbon atoms, and preferably about 9 or 10 carbon atoms, with saturated acids being preferred. Another method involves the utilization of aliphatic diacids that have between 4 and 8 carbon atoms. Diacids with 6 carbon atoms, such as adipic acid, are preferred. In addition, one method details the use of saturated aliphatic dibasic acids that are derived from straight chain paraffin hydrocarbons such as oxalic acid, malonic acid, dimethyl malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. It is stated that aliphatic carboxylic acids that contain heteroatoms in their aliphatic chain, such as diglycollic acid and thio-diglycollic acid, may also be employed. Two unsaturated acids which contain 4 carbon atoms, maleic acid and fumaric acid, are also mentioned.
The present invention utilizes solid state polymerization techniques to overcome the problems arising in the preparation of polyestercarbonates found in traditional interfacial or melt methods, and provides further surprising properties. These and further objects of the invention will be more readily appreciated when considering the following disclosure and appended claims.
In one aspect the present invention relates to a method for preparing a polycarbonate copolymer, prepared by solid state polymerization by preparing a mixture comprising partially crystalline bisphenol A polycarbonate oligomer and at least one source of additional structural units capable of forming ester linkages, and then subjecting the mixture to solid state polymerization to afford a polyestercarbonate. The present invention further employs a method of incorporating an aromatic triacid branching agent by SSP to produce branched polyestercarbonates.
The present invention may be understood more readily by reference to the following detailed description of preferred embodiments of the invention and the examples included herein. In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.
The singular forms xe2x80x9caxe2x80x9d, xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise.
xe2x80x9cOptionalxe2x80x9d or xe2x80x9coptionallyxe2x80x9d mean that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.
As used herein the term xe2x80x9cinterfacial processxe2x80x9d refers to a process comprising the simultaneous use of water and a water immiscible solvent.
The term xe2x80x9cpolyestercarbonatexe2x80x9d as used herein refers to a polymer comprising both carbonate and ester linkages in the polymer chain.
As used herein the term xe2x80x9caromatic radicalxe2x80x9d refers to a radical having a valence of at least one comprising at least one aromatic group. Examples of aromatic radicals include phenyl, pyridyl, furanyl, thienyl, naphthyl, phenylene, biphenyl. The term includes groups containing both aromatic and aliphatic components, for example a benzyl group.
As used herein the term xe2x80x9caliphatic radicalxe2x80x9d refers to a radical having a valence of at least one comprising a linear or branched array of atoms which is not cyclic. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of aliphatic radicals include methyl, methylene, ethyl, ethylene, hexyl, hexamethylene and the like.
As used herein the term xe2x80x9cdiacid soft blockxe2x80x9d refers to an aliphatic diacid which is not a xe2x80x9cbranched diacid.xe2x80x9d Examples of diacid soft blocks are dodecanedioic acid and sebacic acid.
As used herein the term xe2x80x9ccycloaliphatic radicalxe2x80x9d refers to a radical having a valance of at least one comprising an array of atoms which is cyclic but which is not aromatic. The array may include heteroatoms such as nitrogen, sulfur and oxygen or may be composed exclusively of carbon and hydrogen. Examples of cycloaliphatic radicals include cyclcopropyl, cyclopentyl cyclohexyl, tetrahydrofuranyl and the like.
As used herein the term xe2x80x9cbranched diacidxe2x80x9d refers to diacids prepared by oxidative carbonylation of an olefin-containing monoacid. For example oxidative carbonylation of oleic acid gives a mixture of 9- and 10-carboxy stearic acid, said diacids being referred to as xe2x80x9cbranched diacids.xe2x80x9d
In one aspect, the present invention relates a method of incorporating into polycarbonate chains via SSP structural units derived from diacids, and their derivatives, having structure I
xe2x80x83R2O2Cxe2x80x94R1xe2x80x94COOR2xe2x80x83xe2x80x83I
wherein R1 is a C4-C30 aromatic radical optionally substituted by one or more halogen atoms, C1-C10 alkyl radicals or CO2R4 groups; or a C1-C40 aliphatic radical, or a C5-C30 cycloaliphatic radical, and R2 is a C4-C30 aromatic radical.
Structure I includes diacid soft blocks such as dodecanedioic acid, cis-octadec-9-enedioic acid and sebacic acid; aromatic diacid such as terephthalic acid, cycloaliphatic diacids such as 1,4-cyclohexanedicarboxylic acid; and branched diacids. Branched diacid blocks are incorporated into polycarbonates via SSP. Branched diacids that are suitable for incorporation under the conditions of the invention can readily be obtained from the catalytic carboxylation of unsaturated monoacids, such as oleic acid. For example, the known catalytic carboxylation of oleic acid affords a mixture of diacids bearing an octyl (9-carboxy stearic acid) or nonyl (10-carboxy stearic acid) group in the position adjacent to one of the carboxyl groups.
Structure I also includes ester derivatives which are found to be especially suited to copolymer formation with bisphenol A polycarbonate under SSP conditions. Phenyl esters are preferred.
Structure I further includes fully aromatic triacids and their ester derivatives. When an aromatic triacid or its ester derivative is reacted with polycarbonate under the conditions of the present invention a branched polyestercarbonate is obtained. This process yields effective branching in the product polyestercarbonate and potentially superior physical characteristics over previously disclosed branched polycarbonates.
In another aspect, the present invention relates a method of incorporating into polycarbonate chains via SSP structural units derived from hydroxy acids, and their ester derivatives, having structure II
xe2x80x83HOxe2x80x94R3xe2x80x94COOR4xe2x80x83xe2x80x83II
wherein R3 is a C4-C30 aromatic radical and R4 is hydrogen or a C4-C30 aromatic radical.
The hydroxy acid II is preferably p-hydroxybenzoic acid or more preferably phenyl p-hydroxybenzoate which may be reacted with low molecular weight polycarbonate oligomers under SSP conditions to afford high molecular weight carbonate incorporating structural units derived from p-hydroxybenzoate.
The method of the present invention employ a catalyst and diphenyl carbonate in the production of polyestercarbonates that demonstrate advantageous properties relative to analogous simple polycarbonates.
The improved polyestercarbonates of the present invention employ bisphenol A polycarbonate as the polycarbonate source. Typically the polycarbonate is low molecular weight (weight average molecular weight MW of less than 10,000 daltons) oligomeric bisphenol A polycarbonate, referred to herein as xe2x80x9cR-2xe2x80x9d which is prepared by the melt reaction of bisphenol A with diphenyl carbonate in the presence of a catalyst such as sodium hydroxide at a temperature in a range between about 180xc2x0 C. and about 350xc2x0 C.
The present invention preferably employs Sb2O3 as a catalyst. The catalyst system performs two distinct and important functions. First, it serves as an effective nucleating agent for the crystallization of the starting molten blend of diacid, diphenyl carbonate, and amorphous polycarbonate. In this way, the catalyst affords a partially crystalline material which retains substantial crystalline and amorphous polycarbonate phases. In addition, in the amorphous regions of the material, the catalyst system effectively catalyzes the reaction of carbonate and acid groups to produce ester linkages and chain growth under SSP conditions. The catalyst and method of this invention are generally applicable to the preparation of numerous different types of polyestercarbonates that incorporate structural units derived from structures I or II.
The polyestercarbonate made by the method of the present invention generally has a weight average molecular weight (MW) in a range between about 15,000 and about 40,000 daltons, and preferably in the range of about 15,000 to 30,000 daltons, and a glass transition temperature between 85xc2x0 C. and 160xc2x0 C., and preferably between 100xc2x0 C. and 150xc2x0 C.